Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$210.28	10.123%	$231.5666	$231.57	$231.55	$231.60
Purchase #2	$18.94	7.557%	$20.3713	$20.37	$20.35	$20.40
Purchase #3	$141.34	8.210%	$152.944	$152.94	$152.95	$152.90
Purchase #4	$155.95	6.314%	$165.7967	$165.80	$165.80	$165.80
Purchase #5	$131.42	7.529%	$141.3146	$141.31	$141.30	$141.30
Purchase #6	$107.94	5.376%	$113.7429	$113.74	$113.75	$113.70
Purchase #7	$91.45	4.495%	$95.5607	$95.56	$95.55	$95.60
7 purchase totals =	$857.32		$921.2968	$921.29	$921.25	$921.30